More and more frequently, the transmission of information is effected in an optical form by means of networks of optical fibers interconnected by couplers and/or connectors. Despited their inherent advantages as regards the width of the passband, the slight attenuation of optical fibers (.perspectiveto.1 dB per km), the small spatial requirement and light weight, excellent electrical insulation, sound chemical resistance, immunity to electromagnetic interference, as well as the absence of radiations, the known systems for transmitting optical information nervertheless have a certain number of drawbacks.
In actual fact, the power emitted by the transmitters of these systems (for example, electroluminescent diodes) is generally limited with the result that it is necessary to provide high-performing amplifiers at the receivers (for example, PIN diodes), so that the power recived after attenuation of the couplers and connectors is sufficient in order to avoid any excessively high bit error rate. In addition, in particular when such a system comprises a large number of "subscriber" (that is a large number of transmitters and/or receivers), this being the case on board an aircraft, the optical path between an transmitter and a receiver is variable depending on the respective positions of said transmitter and said receiver in said system. Thus, it is necessary to provide gain adjustment means at the receivers so as to adjust the amplitude of the input signal of a receiver in order to correct the influence of the path followed by the information through the system.
These gain adjustment means thus render the receivers complex and greatly complicate implementing components and installing the system. In addition, these means significantly increase costs and reduce reliability.
Thus, it can be seen that in known systems, a high number of subscribers is antinomic of the notion of receivers without any gain control.